diff --git a/tests/phpunit/tests/admin/includes/misc/wpRefreshHeartbeatNonces.php b/tests/phpunit/tests/admin/includes/misc/wpRefreshHeartbeatNonces.php
new file mode 100644
index 0000000000000..fe8e41d36b7c6
--- /dev/null
+++ b/tests/phpunit/tests/admin/includes/misc/wpRefreshHeartbeatNonces.php
@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * Tests for the wp_refresh_heartbeat_nonces() function.
+ *
+ * @group admin
+ * @group misc
+ *
+ * @covers ::wp_refresh_heartbeat_nonces
+ */
+class Tests_Admin_Includes_Misc_WpRefreshHeartbeatNonces extends WP_UnitTestCase {
+
+	/**
+	 * Tests that wp_refresh_heartbeat_nonces() correctly adds nonces to the response.
+	 *
+	 * @ticket 65199
+	 */
+	public function test_wp_refresh_heartbeat_nonces() {
+		$response = array( 'some_data' => 'value' );
+
+		$result = wp_refresh_heartbeat_nonces( $response );
+
+		$this->assertArrayHasKey( 'rest_nonce', $result, 'The response should contain the rest_nonce.' );
+		$this->assertArrayHasKey( 'heartbeat_nonce', $result, 'The response should contain the heartbeat_nonce.' );
+		$this->assertSame( 'value', $result['some_data'], 'Existing data in the response should be preserved.' );
+
+		$this->assertNotFalse( wp_verify_nonce( $result['rest_nonce'], 'wp_rest' ), 'The rest_nonce should be valid for "wp_rest".' );
+		$this->assertNotFalse( wp_verify_nonce( $result['heartbeat_nonce'], 'heartbeat-nonce' ), 'The heartbeat_nonce should be valid for "heartbeat-nonce".' );
+	}
+
+	/**
+	 * Tests that wp_refresh_heartbeat_nonces() overwrites existing nonces if they are already present.
+	 *
+	 * @ticket 65199
+	 */
+	public function test_wp_refresh_heartbeat_nonces_overwrites_existing() {
+		$response = array(
+			'rest_nonce'      => 'old_rest_nonce',
+			'heartbeat_nonce' => 'old_heartbeat_nonce',
+		);
+
+		$result = wp_refresh_heartbeat_nonces( $response );
+
+		$this->assertNotEquals( 'old_rest_nonce', $result['rest_nonce'], 'The rest_nonce should be updated.' );
+		$this->assertNotEquals( 'old_heartbeat_nonce', $result['heartbeat_nonce'], 'The heartbeat_nonce should be updated.' );
+
+		$this->assertNotFalse( wp_verify_nonce( $result['rest_nonce'], 'wp_rest' ), 'The rest_nonce should be valid for "wp_rest".' );
+		$this->assertNotFalse( wp_verify_nonce( $result['heartbeat_nonce'], 'heartbeat-nonce' ), 'The heartbeat_nonce should be valid for "heartbeat-nonce".' );
+	}
+}